Is there any special reason that you use LoH? (Like you really need the fire res?)
Else, I'd switch those for a pair of crafted gloves, which easily can get 20ias/knockback and other mods beside that to sweeten it up.
If you do that, you can remove the nef, and put in a shael. You might also want to think about socketing the armor you use with an ias jewel if really needed.
I don't really know the bow ias bp's for pallys though, you might want to check those out first to see if it's really worth it. :shocked:

Anyway, knockback can be found on crafted gloves, so you can use the widowmaker socket wiser imo.

This is not the right forum for price checks, however I doubt they'll be costy.
Scan your local trade forum and see, or put up an ISO: post in the trade forum. Also, if you do have a good economy, make sure to ask for other useful mods as well.